A linear motor having a conventional thrust generating mechanism is shaped to be a cut-open rotating machine and large attraction works between a mover made up of a magnet pole row and an armature. Patent document 1 discloses a linear motor in which magnetic poles having a first polarity and second polarity are arranged alternately to cancel out the magnetic attraction. In the conventional art, armature magnet pole pitch has been a constant value as shown in FIG. 4 of patent document 1.    Patent document 1: Japanese Patent Laid-open No.